1. Field of the Invention
The invention relates to a catheter used to deliver laser energy from an excimer laser to a lesion within an arterial system or to a body organ. The catheter is particularly suited for use in endovascular therapy to ablate calcified or non-calcified deposits in atherosclerotic lesions.
2. Discussion of Related Art
U.S. Pat. No. 5,429,604 and U.S. Pat. No. 4,844,062 reveal that fiber optic catheter assemblies have increasingly been used for probing and clearing obstructions in various vessels such as arteries. The size of the vessel and the distance from the insertion point to the critical region in the vessel determine the characteristics of the catheter to be used. For example, in some situations it is desirable to insert a very thin catheter a considerable distance into a vessel. The catheter must be quite flexible so that it may be steered considerable distances through winding vessel passages.
The excimer laser enables the disintegration of targeted tissue and can yield relatively pure disintegration without excessive thermal damage to otherwise healthy tissue. The excimer laser is a combination of argon fluoride or krypton chloride and a rare earth gas. This combination forms a laser beam having a very short wavelength and hence photons of very high energy;
Excimer catheters for endovascular therapy are presently produced by the Spectranetics Corporation in the United States. Presently approved laser catheters in the United States for endovascular therapy range in diameter from 1.4 mm to 2.2 mm. The energy output, for ablating atherosclerotic tissue in coronary or peripheral arteries has a fluence of 60 mJ/mm2, 40 Hertz.
The ablation of atherosclerotic lesions by excimer laser energy transforms the lesions into water and carbon dioxide. A gas bubble forms at the laser catheter tip and expands rapidly, which stretches the vessel wall. The abrupt stretch can result in dissection and even occlusion of the vessel.
Calcium can not be ablated with commercially available catheters. Spectranetics has recently developed an excimer laser with more densely packed optical fibers, which results in a decrease of dead space and a higher energy output of a fluence of 80-mJ/mm2 or more, 40 Hertz or more. This recently developed excimer laser enables laser catheters to ablate calcium, but the higher energy output increases the likelihood of dissections. Also, existing laser catheters are relatively stiff, which precludes them from negotiating acute bends, which are common in arterial systems or in body organs.
It is desired that an excimer laser catheter be provided that is capable of being used to ablate hard, calcified areas and which may negotiate acute bends in the arterial system.
One aspect of the invention resides in an apparatus and method for providing endovascular therapy. The apparatus includes an elongated catheter containing optical fibers arranged in a concentric manner, the catheter having a tip whose diameter is smaller than a remainder of the catheter, the tip having a length of at least 1 cm and a diameter of less than 1 millimeter. The apparatus preferably also includes an excimer laser connected to the optical fibers capable of delivering laser energy through the optical fibers. The method also includes the step of inserting the catheter through an artery by pushing the same until the tip is in within laser energy striking distance of a lesion for ablating the same. For treatment of heavily calcified lesions, the excimer laser should be capable of delivering laser energy at higher energy levels in excess of a fluence of 60-mJ/mm2 and in excess of 40 Hertz. For treatment of non-calcified lesions, the excimer laser need only be capable of delivering laser energy at lower energy levels, i.e., a fluence of 60 mJ/mm2 or less at 40 Hertz or less.